1. Field of the Invention
The present invention relates generally to an image forming apparatus such as a copier, a facsimile apparatus, or a printer which employs the electrophotography technique.
The invention also relates generally to a toner transport mechanism used in such an image forming apparatus, and more particularly to a toner transporting device which is disposed along a toner transport path which passes between a developing device for supplying toner to a surface of a photosensitive body and developing a latent image on the surface of the photosensitive body to form a toner image, and a cleaning device for removing and recovering residual toner adhering to the surface of the photosensitive body surface, and which transports residual toner recovered by the cleaning device to the developing device after a toner image formed by the developing device is transferred to a sheet.
Furthermore, the invention also relates generally to a toner tank for supplying toner from the outside to an image forming apparatus.
2. Related Art
Generally in a developing device using toner, a latent image formed on a surface of a photosensitive body in accordance with recording information must be provided. A toner supply container must be provided which is comparable in length to that of the developing device to supply toner uniformly and continuously at a uniform density to the entire effective image area. Thus, the toner supply container occupies a substantially large space within the machine. A further space (a cleaning unit) for collecting and storing unused toner supplied to the effective image area must be provided separately.
Japanese Patent Publication (Kokoku) No. SHO52-382 discloses a novel way to cope with this space problem. This technique employs a toner transport mechanism which circulates in a path which includes a developing unit and a cleaning unit. A magnetic brush for recovering toner is formed by carriers transported to the cleaning unit by the transporting mechanism. Toner which has been recovered from a surface of a photosensitive drum which was not transferred (hereinafter untransferred toner) is returned to the developing unit to be reused. The technique is advantageous in that the quantity of new toner which must be supplied can be reduced, and that the space for storing recovered toner can be reduced in size.
However, since recovered toner and fresh toner must be stirred and mixed in this apparatus, an agitator and a toner hopper for supplying fresh toner must be provided with the developing unit. In this respect, there is a limit in device size reduction and in device layout freedom.
Another known toner transport mechanism has a configuration shown in FIG. 30 (Japanese Patent Publication (Kokai) No. SHO63-246780). FIG. 30(a) is a plan view of the device, FIG. 30(b) is a fragmentary cross sectional view taken along lines 30(b)--30(b) of FIG. 30(a), FIG. 30(c) is a fragmentary cross sectional view taken along lines 30(c)--30(c) of FIG. 30(a), and FIG. 30(d) is a cross sectional view taken along lines 30(d)--30(d) of FIG. 30(a).
As shown in these figures, the toner transport mechanism comprises a strip member 24, and toner removing device L. The strip member 24 is elongated and is circulated between the interior of a developing device M for supplying toner to a surface of a photosensitive drum 23. The developing device develops an image on the surface of the photosensitive drum 23 to form a toner image, and the interior of a cleaning device N removes and recovers residual toner, which adheres to the surface of the photosensitive drum 23 after the toner image formed by the developing device M is transferred to a sheet. The toner removing device L removes residual toner adhering to the surface of the strip member 24 in the cleaning device N.
The strip member 24 is composed of sponge made of a porous elastic body. A reinforcing core member 25 is embedded in the center portion of the strip member. The strip member 24 passes through the interior of covers 26a and 26b which extend between a body case 32 of the developing device M and a body case 34 of the cleaning device N. Strip member 24 is supported in a circulatable manner by a driving pulley 27a and driven pulleys 27b, 27c and 27d, so as to be circulated in the direction indicated by arrow 28 by driving pulley 27a. As more particularly shown in FIG. 30b, driving pulley 27a is coupled to a shaft 27e supporting a drive gear 29, in turn coupled to motor 30.
The toner removing device L, is formed of a plurality of blades 31 arranged in body case 32 of the developing device, so as to oppose each other across the strip member 24 which runs in the direction indicated by arrow 8 inside body case 32. A semicircular notch 31a is formed in the front end portion of each of the blades 31 which engage with the surface of strip member 24.
In the toner transport mechanism having this configuration, a developing roller 33 disposed in the developing device M is rotated to cause toner to be supplied to the surface of the photosensitive drum 23. The toner adheres to a latent image which is electrostatically formed on the surface of the photosensitive drum 23, thereby forming a toner image. After the toner image is transferred to a sheet which is not shown, residual toner adhering to the surface of photosensitive drum 23 is scraped off by a cleaning blade 35 disposed in cleaning device N so as to slidably contact the surface of photosensitive drum 23. The residual toner recovered by the scraping operation adheres to the surface of the strip member 24 and is transported from the interior of the cleaning device N to the interior of the developing device M through the interior of cover 26b. The toner is then scraped off by blades 31 into body case 32 of developing device M. Strip member 24 from which the residual toner has been scraped off is circulated in the direction indicated by arrow 28 to proceed again toward the interior of the cleaning device N.
However, this toner transport mechanism has the following problems:
(a) Strip member 24 is composed of sponge made of a porous elastic body. Toner is transported by adhering to the surface (mainly to a number of pores) of the sponge. This is not an efficient way to transfer toner.
(b) Toner adhering to the surface of strip member 24 is scraped off by blades 31. When strip member 24 is not sufficiently scraped by blades 31, the pores on the surface of strip member 24 clog with toner so that transportation of the toner is even less efficient.
(c) Toner adhering to the surface of strip member 24 is scraped off by blades 31 disposed inside developing device M. This requires the developing device to be relatively larger and complicated. In turn the entire image forming apparatus must be enlarged to the same degree as the developing device must be enlarged.
In addition, other problems with the prior art arise. Powdered toner used in the image forming apparatus increases in density if allowed to stand unagitated for a long period, and easily solidifies. It is more difficult to supply toner to the image forming apparatus once it solidifies. As a result the obtained images are blurred, and the print quality is impaired. Therefore, while supplying toner to the image forming apparatus during printing, the toner must be stirred to prevent solidification.
FIG. 31(a) shows an example of a toner tank. During the printing process, agitators 42 disposed in toner container 41 rotate in the direction indicated by arrows I, and stir toner (not shown) contained in toner container 41, breaking blocks of toner and improving the fluidity of the toner. Furthermore, the rotation of agitators 42 supplies toner through a toner supply port 41-1 to an image forming apparatus (not shown) which is located below container 41.
FIG. 31(b) is a cross-sectional view of the toner tank of FIG. 31(a). The outer periphery of rotation loci of the agitators 42 is shown by two-dot chain lines, 43. The hatched portion 0 in FIG. 31(b) is outside the rotation loci of the agitators 42, and toner in this hatched portion O is hardly stirred.
Thus, toner is unevenly stirred and blocks of toner are liable to remain unbroken in the toner tank. This causes an insufficient amount of toner to be supplied to the image forming apparatus, resulting in blurred images and impaired print quality. In addition, excess toner will collect in the hatched portion O outside the rotation loci of agitators 42. Since the bottom of the toner container is substantially horizontal, this toner is unusable, and is wasted. Wasting this toner which will not be supplied to the image forming apparatus is uneconomical.